Electric protective system.



ERIC GR'DDN VATERS, GF FOREST ROV?, ENGLAND.

ELECTRIC PRGTEC'SVE SYSTEM.

Specification of Letters Patent.

Patented Aug. 3i, 1915.

Application filedjlrpril 27, 1915. Serial No. 24,378.

T0 all whom it may] concern:

Be it known that l, Emo GORDON -WU-rivalss, a subject of the King of Great Britain and Ireland, residing at Forest Row, in the county of Sussex, England, have invented Improvements in or Relating to Electric Protective Systems, of which. the following is a specification.

This invention relates to the protection of electric systems formed in sections, or capable of being so divided, for instance, ring main systems.

lt has been proposed in order automatically to cut out at one end faulty feeders employed in connection with a three-phase alternating current system in which the neutral point is earthed, to provide each feeder cable with a switch operable by leakage current traversing a trip coil, the latter being connected between an insulsl ted sheath and.

earth. Such an arrangement if applied to electric systems formed in sections (for example ring main schemes in which faulty cables should be cut out at both ends) possesses this disadvantage that on the cccur rence of a fault in one of the sections other,

sections would be liable to be cut out by extraneous current traversing the relay circuit.

The object of the present invention is to provide a convenient means of cutting' out both ends of faulty cable sections free of the above disadvantage.

The invention consists in the provision in an electric protective system wherein cutting out of faulty sectionsis edected by :ault current, of two separate protective conductors for each cable section, the respective protective conductors being in connection with tripping means at the ends of the cable section and `disposed in proximity to the cable section.

In the yaccompanying drawings, Figure l is a diagrammatic View of a ring main system protected in accordance with'the invention; Fig. 2 is a diagrammatic View representing in cross section one of the cable sections of such system.

In carrying the invention into effect in the formillustrated by way of example, two protective conductors c c1 constituted as earth shields, are provided for each section of a ring main including substations o and mains c, each protective conductor being earthed by way of a relay g. Circuit breakers l are provided and are arranged to be operated by snit-able trip coils controlled by the relays, such trip coils being exemplified at c as included in a .local battery circuit f. lncperation when the whole system is working properly and the insulation of the desired part complete, no current other than possible static charging current can liow Y through the relays g either from earth or ir'rom the cable. Should a fault occur on one section of the ring main, however, current flows from the generating station A around both limbs of the system, uniting at thc fault and flowing to earth through the two protective conductors e and e1 and relays g. The arrangement is such that even in the case of a dead earth on the cable, 'that is a fault such that the resistance of the path from the fault to earth is very low, suflicient current will always flow through the conductors e and c1 and through the relays g owing to the mutual induction eiiect of the fault current passing through the feeder cable orwmain and `feeding the fault. The two relays of a faulty section are thus 0perated and the iaulty section cut out.

lt will he understood that none of the fault current passing to the generating station through earth can possibly traverse the relays or' other sections because their circuits are not completed. For this reason perfect discrimination between faulty and healthy sections is insured.

The conductors c and e1 can be formed in any convenient way by suitable lead or other metallic coverings to be cabled, insulated from each other and from earth, as shown in Fig. f2., and divided at the various substa tionsu The invention need not necessarily be employed in connection with ring main systems but can be applied to any scheme in which sections are provided or can be used.

lVhat l claim is zl. ln an electrical distribution system comprising cable sections adapted to be discriminately cut out by fault current, th combination with each cable section or a switch at each end thereof, two separate protective conductors and two sets of switch tripping means, one such set of tripping means being associated with one of the protective conductors and the other set of tripping means being associated with the other protective conductor.

2. ln an electrical distribution system connai-icing cable sections adapted to be discriminately cut out by fault current, the

eenbmton with each Cable sectnn and :1 Switch ai; each end thereof, of 'two Separate protective conductors flisposed in proximity to he, cable section, one such pmi-active con finster being emthed und neludng a reny 21TH.' ged near one end of the ezxne saeetmn and v7ne nher protectlve conductor belng em'ted an also including a reay arranged nem he opposite end the Cabic section, i'eu's associated with such reays and 's in the 10e-n1 cfens adapted to opches when a 'fault occurs, the .u passing to earth from the cable, L fhe separate protect-ive con- ;znc; associated 'days.

an e'ec'ca distribution Sjef-Sem sing cable sections adapted 0 be clis- ERE@ GORDU VATER'S.

vtness z R. AT. BARE-1.1.? 

